Combobox selection loading previous selection - c++

Question

I have a combobox containing "1,2,3,4,5". When I make a selection in my combobox, the previous selection is loaded. For example, if the value in the combobox is "1" and I select "2", "1" is loaded into my variable nApplication and "2" will be displayed on my combobox. If i want to load "2", I need to change the selection one more time. Example change from "2" to "3". How do I make it load the number I select? My code looks like this.
void CAppDlg::DoDataExchange(CDataExchange* pDX)
{
DDX_Text(pDX, IDC_Application, nApplication);
.
.
void CAppDlg::OnCbnSelchangeapplication()
{
UpdateData(TRUE);
int j = nApplication-1;
for(int i=0; i<MAX_LABEL; i++){
bool bShow = i < arrLabel[j];
((CButton *)GetDlgItem(IDC_Label1+i))->ShowWindow(bShow);
}
}
Any help would be appreciated. Thanks.

Answer 1

As explained in my comments, I suspect that the contents of the combo-box are updated after the CBN_SELCHANGE message is processed, and that's what causing you problems. Therefore a workaround could be post a custom (application-defined) message, to be processed later.
The type of the function must be afx_msg LRESULT (CWnd::*)(WPARAM, LPARAM) (check the documentation).
So, in your class declaration, add:
public:
afx_msg LRESULT OnComboSelChanged(WPARAM wParam, LPARAM lParam);
In your message-map:
ON_MESSAGE(WM_APP+100, OnComboSelChanged)
And finally the implementation:
void CAppDlg::OnCbnSelchangeapplication()
{
// Place a message in the message queue
PostMessage(WM_APP+100);
}
LRESULT CAppDlg::OnComboSelChanged(WPARAM wParam, LPARAM lParam)
{
UpdateData(TRUE);
int j = nApplication-1;
// I have simplified your code a little
for(int i=0; i<MAX_LABEL; i++)
GetDlgItem(IDC_Label1+i)->ShowWindow(i < arrLabel[j]);
return 0L;
}
However, all this, ie calling UpdateData(TRUE);, get the string there, convert it to int and take actions depending on its value, may just be an overkill, esp if the combo-box contains just a contiguous number-range (1..5 in your case). UpdateData(TRUE); transfers the values in ALL your controls to variables, and this may just not be needed. It seems to be a mechanism controlling the appearance of other controls, it's not really "data-entry" (I guess the combod-box is a non-editable drop-down list). So, you could just not use DDX/DDV at all, instead check the selected item yourself. It's a zero-based index. Here is the code:
void CAppDlg::OnCbnSelchangeapplication()
{
// Get selected item
int j = ((CComboBox *)GetDlgItem(DC_Application))->GetCurSel();
if (j == CB_ERR) return;
for(int i=0; i<MAX_LABEL; i++)
GetDlgItem(IDC_Label1+i)->ShowWindow(i < arrLabel[j]);
}
Please note that the code fragments above have not been tested, it's just what I would do.